The present invention relates to a network system capable of setting at one time a plurality of connections for one call, and to a switching unit.
The multimedia services of an HDTV (High Definition TV) etc consist of a plurality of media elements such as images, voices an texts etc. In the case of transmitting the multimedia services via an ATM (Asynchronous Transfer Mode) network, QOSs (Qualities of Services) required of the respective media elements is different per media element.
In view of this point, in the instance given above, a setting way is not that one connection for transmitting all the media elements is set, but that a connection is set for every media element. If done in this way, each of the medial elements can be transferred. in accordance with a nature (of e.g., whether or not data are transferred burstwise, etc) of each medial element. Therefore, the ITU-T is examining a communication method of setting the connection for every media element. According to this communication method, there is set one call for which to set a plurality of connections. This call is known as a "plurality-of-connection call".
Incidentally, the plurality-of-connection call set in the ATM network is established only when all of the QOSs of the respective connections are satisfied between call-out a DTE (Data Terminal Equipment) of the multimedia service and a call-in DTE of the data. FIG. 37 (a) is an explanatory diagram showing an example in which the plurality-of-connection call is not established in a network system. FIG. 37 (b) is an explanatory diagram showing an example where the plurality-of-connection call is established in a network system.
FIG. 37 (a) and FIG. 37 (b) show an example of the network system in which data about, e.g., movies as a multimedia service are transferred from a call-out DTE 1 via ATM switching units (ATM-SWs) 3 and 4 to a call-in DTE 2. In this example, the movie data consist of media elements such as image data, voice data and text (subtitles) data.
In this example, when the movie data is transmitted by the call-out DTE 1 to the ATM-SW 3, the requests to satisfy the QOSs(which are, e.g., ensuring of a bandwidth, a cell arrival interval, or a delay time of a data transfer etc) of respective pieces of the data give to the ATM-SWs 3 and 4. In response thereto, the ATM-SWs 3 and 4, as shown in FIG. 37(a), satisfy the QOSs relative to, e.g., the image data and the voice data but do not satisfy the QOS relative to the text data. In this case, the ATM-SWs 3 and 4 execute a call disconnecting process even if possible of establishing the connections regarding the image data and the voice data. Accordingly, the plurality-of-connection call is not established between the DTE 1 and the DTE 2.
By contrast, as shown in FIG. 37 (b), the ATM-SWs 3 and 4 satisfy the QOSs relative to the image data, the voice data and the text data, in which case the connections for transmitting each of the data is set between the DTEs 1 and 2. The plurality-of-connection call is thereby established between the DTEs 1 and 2, and the movie data are transmitted to the call-in DTE 2 from the call-out DTE 1.
Thus, the establishment of the plurality-of-connection call requires establishing all the connections for transmitting the respective media elements. This being the case, the applicant of the present application made an application of an ATM-SW (Japanese Patent Application No. 5-180540: hereinafter referred to as the "preceding application") for obviating the above problem prior to filing the present application. FIG. 38 is an explanatory diagram illustrating the ATM-SW relative to the preceding application.
FIG. 38 shows a network system using the ATM-SW concerning the preceding application. Then, there is given an illustration of how the image data and the voice data are transferred from a DTE 5 to a DTE 6. Referring to FIG. 38, in the case of establishing the plurality-of-connection call for transmitting the image data and the voice data between, e.g., the DTE 5 and the DTE 6, an ATM-SW 8 and an ATM-SW 9 establish the respective connections along a route I on which the data are transmitted in a sequence such as DTE 6.fwdarw.ATM-SW 9.fwdarw.ATM-SW 8.fwdarw.DTE 5.
At this time, if the QOS needed for transmitting the voice data on, e.g., the route I is not satisfied (if the connection for transmitting, e.g., the voice data is not established on the route I due to a deficiency of bandwidth etc), the ATM-SWs 8, 9 and 10 establish connections for transmitting the voice data along a route II on which the data are transmitted in a sequence such as DTE 6.fwdarw.ATM-SW 9.fwdarw.ATM-SW 10.fwdarw.ATM-SW 8.fwdarw.DTE 5. Thus, the ATM-SWs 8, 9 and 10 set separate paths such as the route I and the route II and establish the respective connections. The plurality-of-connection call is thereby established.
There arise, however, the following problems inherent in the network system pertaining to the above preceding application. To be specific, under a condition shown in FIG. 38, if impossible of satisfying the QOS of the voice data between the ATM-SW 9 and the DTE 6 when trying to establish the connection of the route II, the path for the voice data on the route II can not be set. Accordingly, the connection could not be established by use of the route II, and the plurality-of-connection call could not be established.
Further, in the network system according to the preceding application, if the plurality-of-connection call is set on the route I and the route II as well, it is required that the DTE 5 should make the ATM-SW 8 recognize that the respective connections belong to the same call. It is therefore required that the DTE 5 be constructed to transfer and receive identifying data for specifying the plurality-of-connection call between the ATM-SW 8 and the DTE 5 itself. Accordingly, the use of the ATM-SW relative to the preceding application must involve the use of the DTE 5 having the above-described construction or must add the same construction to the conventional DTE 5.